1. Field of the Invention
The present invention relates to a light coupled device such as a 2-channel photocoupler having a plurality of light couplings.
2. Description of the Related Art
A signal transmitting interface in factory automation equipment or the like requires electrical insulation from external devices, and besides is used in an environment filled with influence of external noise, and accordingly a photocoupler is used as the signal transmitting interface. The photocoupler used in the interface must have a high-speed performance (high-speed signal transmission), and a plurality of photocouplers are required since the interface has a plurality of inputs and outputs. Generally, multi-channel type light coupled devices are used, each of which includes a plurality of light couplings in one package.
One example of such multi-channel type light coupled devices is shown in FIGS. 4A through 4C, 5 and 6.
FIGS. 4A through 4C show an outward appearance of a conventional multi-channel type light coupled device, in which FIG. 4A is a front view, FIG. 4B a side view and FIG. 4C a plan view. FIG. 5 is a view showing an interconnection in the light coupled device shown in FIGS. 4A through 4C. FIG. 6 shows a layout of a lead frame on the light receiving side as shown in FIG. 5.
To realize a high-speed performance, the 2-channel type light coupled device shown in FIGS. 4A through 4C, 5 and 6 employs light receiving elements each having a photodiode and a light signal processing circuit integrated into a single chip by bipolar IC process. Each light receiving element, acting as an element on the output (or secondary) side, has three external connectors, i.e. a source voltage terminal Vcc, a GND terminal and an output terminal Vo. In this example, two light receiving elements 2A and 2B are provided. Since the two light receiving elements can share the source voltage terminal Vcc and GND terminal, a connecting method may be employed therefor, as shown in FIG. 6, in which light receiving elements 2A and 2B are connected through a metal wire to a lead frame 3 to connect the source terminal Vcc of the light receiving elements 2A and 2B to the external terminal Vcc leading to the lead frame 3. Thus, while the two light receiving elements 2A and 2B each with three external connectors are built in, this construction requires a total of only four external terminals which are the common source voltage terminal Vcc, an output terminal Vol (i.e. output terminal of light receiving element 2A), an output terminal Vo2 (i.e. output terminal of light receiving element 2B) and the common GND terminal.
Where each of the light receiving elements 2A and 2B has three terminals to make a total of six terminals on the secondary side (output side), the result will be a 12-pin package. By sharing certain terminals as noted above, the number of terminals on the secondary side will be four, which provides a simplified package having only eight pins as shown in FIG. 4. In this way, a light coupled device with a plurality of light couplings, generally, has some of the terminals shared by the light receiving elements in order to achieve compactness and low cost of the product.
In a widely used construction of a multichannel type light coupled device, each light emitting element and an associated light receiving element have a transparent silicone resin filled therebetween to form a light coupling which is sealed with an epoxy resin. One such example is shown in FIG. 7.
FIG. 7 is a sectional view schematically showing light coupled sections of a conventional multi-channel type light coupled device.
In FIG. 7, adjacent light couplings 24 are formed of a transparent silicone resin. Light emitted from each light emitting element 1 passes through a light coupling 24 formed of the transparent silicone resin, and directly reaches the opposite light receiving element 2. Part of the light from the light emitting element 1 is reflected from the boundary between the silicone resin and an adjoining epoxy resin 25 to reach the light receiving element 2. In this way, the epoxy resin 25 filled between the two light couplings 24 formed of the transparent silicone resin plays a role of blocking light transmission between the channels so that light emitted from the light emitting element 1 of one channel is prevented from reaching the light receiving element 2 of the other, adjacent channel, in order to avoid an interference of light signals (hereinafter referred to as xe2x80x9ccrosstalkxe2x80x9d) between the two light couplings 24.
The two-channel type light coupled device shown in FIG. 5 requires a construction in which signals inputted to input terminals T1 and T2 result in a signal outputted from an output terminal T7, while signals inputted to input terminals T3 and T4 result in a signal outputted from an output terminal T6.
That is, it is necessary to ensure that the input signals to the input terminals T1 and T2 exert no influence, such as crosstalk, on the output signal from the output terminal T6, and that the input signals to the input terminals T3 and T4 exert no influence on the output signal from the output terminal T7. For this purpose, each light coupling 24 shown in FIG. 7 must be formed of the transparent silicone resin, and the two adjacent light couplings 24 must be spaced apart to be out of contact with each other. This requirement has been a limitational factor in an area saving designing of lead frame size and downsizing (volume saving) of packages.
The present invention has been made having regard to the state of the noted above, and its object is to provide a multichannel type light coupled device with a construction for enabling an area saving designing of lead frame size and downsizing (volume saving) of packages.
In one aspect of the invention there is provided a light coupled device comprising a plurality of light couplings and an insulating and light shielding element disposed between the light couplings arranged adjacent each other.
The light coupled device according to the invention prevents crosstalk since the insulating and light shielding element blocks light transmission between the adjacent light couplings. This construction, compared with the conventional construction (FIG. 7), realizes a reduced distance between the adjacent light couplings.
The insulating and light shielding element used in the light coupled device according to the invention may comprise a polyimide film or silica glass sheet with a light shielding color applied thereto.
A light shield may be effected between the adjacent light couplings by using an insulating and light shielding polyimide film or silica glass sheet. Even though the light couplings are arranged close together, no crosstalk will occur therebetween.
Further, in the invention it is preferable that projections or recesses are formed on/in a lead frame on which the light couplings are mounted, for fixing the insulating and light shielding element to a predetermined position between the light couplings.
In the light coupled device according to the invention, with the projections or recesses formed on/in the lead frame for fixing the insulating and light shielding element to a predetermined position between the light couplings, the light shielding element does not become displaced when a transparent silicone resin is injected to form the light couplings. Consequently, the light shielding element may be fixed to an optimal position in the middle between the adjacent light couplings.
Further, in the invention it is preferable that the insulating and light shielding element is fixed by an adhesive to the lead frame on which the light couplings are mounted.
The insulating and light shielding element may be fixed to the lead frame by using an adhesive such as an epoxy resin, instead of the projections or recesses. With this measure also, the insulating and light shielding element may be fixed to the optimal position in the middle between the adjacent light couplings.
In another aspect of the invention, there is provided a light coupled device comprising a plurality of light couplings, each of the light couplings including, at least, a primary light coupling section and a secondary light coupling section formed of a light transmitting filler around a light emitting element on a primary side and a light receiving element on a secondary side of the light coupled device, and an insulating and light transmitting element disposed between the primary light coupling section and the secondary light coupling section for optically interconnecting the primary light coupling section and the secondary light coupling section.
The light transmitting filler may be a transparent silicone resin.
In the invention it is preferable that the primary and secondary light coupling sections are formed of a transparent silicone resin around the light emitting element on the primary side and the light receiving element on the secondary side, respectively, the primary light coupling section and the secondary light coupling section being optically interconnected through an insulating and light transmitting element, the primary light coupling section, the secondary light coupling section and the insulating and light transmitting element constituting each of the light couplings. the above light coupled device according to the invention, the primary light coupling section and secondary light coupling section formed of a light transmitting filler such as a transparent silicone resin are optically interconnected through the insulating and light transmitting element. This construction realizes an optical path of reduced volume, compared with a case where each light coupling is formed only of a light transmitting filler such as a transparent silicone resin. A sufficient distance is secured between the light couplings for preventing crosstalk therebetween even though the lead frames are reduced in size. Thus, the light couplings may be arranged closer together than in the conventional construction (FIG. 7).
The insulating and light transmitting element used in the light coupled device according to the invention may comprise a silica glass sheet. The insulating and light transmitting element is not limited to a particular shape, but may be cylindrical, spherical or cubic, for example..
The primary light coupling section and secondary light coupling section may be optically interconnected by using a silica glass sheet, which realizes an optical path of reduced volume, compared with a case of forming each light coupling only of the light transmitting filler. By using a cylindrical, spherical or cubic insulating and light transmitting element, the primary light coupling section and secondary light coupling section may be optically interconnected in a uniform way, to realize an optical path of reduced volume.